It is more and more recognised that photovoltaic conversion of solar energy has to become as soon as possible a major source of the world energy supply in the future.
The photovoltaic industry will be a major industry producing solar modules with the square km as a reference area unit. All mature technologies, either based on silicon or on thin film (a-Si, μc-Si, CIGS or CdTe), aim to reach this objective. For this, a key point is to develop large area processing at low module production costs while maintaining, or better, increasing the conversion efficiencies. Junctions based on Cu(In,Ga,Al)(S,Se)2 chalcopyrite absorbers have already demonstrated high conversion efficiencies and compatibility with large area production of efficient modules at the pre-industrial level (D. Lincot et al., Solar Energy 77 (2004) 725-737).
According to WO 00/62347 a solar cell is provided with an absorbing layer which is arranged on a flexible and band-shaped support. The absorbing layer is at least partially provided with components of copper and is provided with at least one element from the group of indium and gallium and with at least one element from the group of selenium and sulphur and is at least partially embodied as p-type. The absorbing layer is at least partially deposited on the support in a plating manner. The components of the absorbing layer are in a stoichiometric ratio in relation to one another. The absorbing layer is heat-treated after having been deposited on the support.
U.S. Pat. No. 7,026,258 B2 concerns a method for making thin-film CIGS which consists in: electrochemically depositing on a substrate a layer of stoichiometry close to CuInSe2; then rapidly annealing said layer from a light source with pulses of sufficient power to recrystallise CIS. The electrodeposited elements are premixed. Thus, after the deposition step, a homogeneous matrix is obtained which can support sudden temperature increases during the rapid annealing.
All these processes involve the preparation of group IB-IIIA-VIA metal alloys and, in particular, alloys comprising copper, indium and selenium.
Coating thin layers of metal by way of electrochemistry is nowadays a well-known and frequently used technique, in particular for depositing copper. Electroless deposition as well as electrodeposition of such a metal has been developed for the purposes of decorative industry, protection against corrosion and for the electronic industry, and has reached a mature stage.
However, the prior art methods for depositing the above mentioned elements suffer from the defect that the ratio of deposited copper to indium is not constant throughout the entire substrate surface. In particular, the variation in the Cu—In atomic ratio is much too high to produce a working solar module on a substrate as large as, for example, 10×10 cm2.